Liquid Crystal Display Device

ABSTRACT

A liquid crystal display device includes first and second substrates with a liquid crystal therebetween, a thin film transistor on the first substrate, a color filter layer of different colored layers between the liquid crystal and the thin film transistor, and an electrode structure layer between the liquid crystal and the color filter layer. The electrode structure layer includes a transparent insulating film, and first and second transparent conductive films formed on opposite sides of the transparent insulating film. The color filter layer includes a first region formed of one colored layer, and a second region formed of at least two laminated different colored layers. The first transparent conductive film covers an upper surface of the color filter layer in both of the first and second regions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/832,246, filed Jul. 8, 2010, the contents of which are incorporatedherein by reference.

The present application claims priority from Japanese application JP2009-162319 filed on Jul. 9, 2009, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device.

2. Description of the Related Art

Conventionally, a liquid crystal display device includes a thin filmtransistor (TFT) substrate on which TFTs for driving liquid crystal isformed and a color filter substrate having a color filter formedthereon, the liquid crystal being sandwiched therebetween. Between theTFT substrate and the color filter substrate, it is required to form agap into which the liquid crystal is filled. In order to retain the gap,a spacer is formed between the TFT substrate and the color filtersubstrate.

There is known a method of forming a spacer by laminating colored layersconstituting the color filter, in a case where the spacer is formed onthe color filter substrate (Japanese Patent Application Laid-open No.2001-117103 (corresponding U.S. Pat. No. 7,248,328)). Further, there isknown a method of forming the color filter on the TFT substrate(Japanese Patent Application Laid-open No. 2000-98422).

When the spacer is formed of the colored layers, it is required to add abarrier layer so that pigments dispersed in the colored layers may notbe dissolved in the liquid crystal. Addition of the barrier layer isrequired also in the case where the color filter is formed on the TFTsubstrate.

SUMMARY OF THE INVENTION

The present invention has an object to provide a liquid crystal displaydevice in which materials dispersed in colored layers are prevented frombeing dissolved in liquid crystal without adding another member.

(1) A liquid crystal display device according to the present inventionincludes: a first substrate; a second substrate; liquid crystal providedbetween the first substrate and the second substrate; a thin filmtransistor formed on a surface of the first substrate facing the liquidcrystal; a color filter layer including a plurality of colored layers,the color filter layer being formed between the liquid crystal and thethin film transistor; and an electrode structure layer for generating anelectric field which is parallel to the first substrate for driving theliquid crystal, the electrode structure layer being formed between theliquid crystal and the color filter layer, in which: the electrodestructure layer includes: a transparent insulating film formed of one ofa semiconductor oxide and a semiconductor nitride, the transparentinsulating film being formed so as to separate a surface of the liquidcrystal and a surface of the color filter layer facing each other; and afirst transparent conductive film and a second transparent conductivefilm both formed of an oxide semiconductor, the first transparentconductive film and the second transparent conductive film being formedon both sides of the transparent insulating film, respectively; thecolor filter layer includes: a first region formed of one colored layerof the plurality of colored layers; and a second region formed of atleast two laminated colored layers of the plurality of colored layers;and the second region has a convex portion formed therein, the convexportion being formed of the at least two laminated colored layers, andthe convex portion retains a gap formed between the first substrate andthe second substrate. According to the present invention, thetransparent insulating film, the first transparent conductive film, andthe second transparent conductive film of the electrode structure layermay prevent the materials dispersed in the colored layers from beingdissolved in the liquid crystal. Further, the transparent insulatingfilm, the first transparent conductive film, and the second transparentconductive film are members required for driving the liquid crystal, andhence it is unnecessary to add another member.

(2) The liquid crystal display device described in Item (1) may furtherinclude a black matrix formed between the color filter layer and thethin film transistor.

(3) The liquid crystal display device described in Item (1) may furtherinclude a black matrix formed between the liquid crystal and the secondsubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an exploded perspective view illustrating a liquid crystaldisplay device according to a first embodiment of the present invention;

FIG. 2 is a schematic plan view illustrating a part of a liquid crystaldisplay panel of the liquid crystal display device illustrated in FIG.1;

FIG. 3 is a plan view illustrating more details of the part of theliquid crystal display panel illustrated in FIG. 2;

FIG. 4 is a cross-sectional view of the liquid crystal display paneltaken along the line IV-IV of FIG. 3;

FIG. 5 is a plan view illustrating a part of a liquid crystal displaypanel of a liquid crystal display device according to a secondembodiment of the present invention; and

FIG. 6 is a cross-sectional view of the liquid crystal display paneltaken along the line VI-VI of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention are described withreference to the accompanying drawings.

First Embodiment

FIG. 1 is an exploded perspective view illustrating a liquid crystaldisplay device according to a first embodiment of the present invention.The liquid crystal display device includes a liquid crystal displaypanel 10. The liquid crystal display panel 10 is supported by an upperframe 12 and a lower frame 14.

FIG. 2 is a schematic plan view illustrating a part of the liquidcrystal display panel 10 of the liquid crystal display deviceillustrated in FIG. 1. FIG. 3 is a plan view illustrating more detailsof the part of the liquid crystal display panel 10 illustrated in FIG.2. FIG. 4 is a cross-sectional view of the liquid crystal display panel10 taken along the line IV-IV of FIG. 3.

The liquid crystal display panel 10 includes a first substrate 16 and asecond substrate 18 (see FIG. 4). Both of the first substrate 16 and thesecond substrate 18 are a transparent substrate (for example, glasssubstrate). Liquid crystal 20 is provided between the first substrate 16and the second substrate 18. Polarizing plates 22 are adhered tosurfaces of the first substrate 16 and the second substrate 18 on sidesopposite to the liquid crystal 20, respectively, in a crossed Nicolsstate.

A thin film transistor (TFT) 24 is formed on a surface of the firstsubstrate 16 facing the liquid crystal 20. The thin film transistor 24serves as a switch for controlling driving of the liquid crystal 20. Thethin film transistor 24 is a bottom gate type thin film transistor, inwhich a gate electrode 26 is formed at a bottom thereof. A scanningvoltage for control is applied to the gate electrode 26. The gateelectrode 26 is formed on the first substrate 16. A gate insulating film28 formed of an inorganic material (semiconductor oxide such as SiO₂ orsemiconductor nitride such as SiN) is formed by, for example,plasma-enhanced chemical vapor deposition (CVD), so as to cover the gateelectrode 26. A semiconductor layer 30 formed of, for example, amorphoussilicon or microcrystalline silicon is formed on the gate insulatingfilm 28. On the semiconductor layer 30, a source electrode 32 to which apixel potential is output and a drain electrode 34 to which an imagesignal is applied are formed. An insulating layer 36 formed of aninorganic material (semiconductor oxide such as SiO₂ or semiconductornitride such as SiN) is formed so as to cover the source electrode 32,the drain electrode 34, and the semiconductor layer 30. The insulatinglayer 36 prevents the semiconductor layer 30 from being contaminated byhumidity.

A black matrix 38 is formed on an upper portion of the thin filmtransistor 24 (on insulating layer 36). That is, the black matrix 38 isformed between the thin film transistor 24 and a color filter layer 40.The black matrix 38 is formed of a resin containing a black pigment orcarbon. The black matrix 38 prevents light from entering a channelregion of the semiconductor layer 30. Therefore, the black matrix 38 hasan island-like or stripe-like shape in plan view.

The color filter layer 40 is formed between the liquid crystal 20 andthe thin film transistor 24 (for example, on black matrix 38 andinsulating layer 36). The color filter layer 40 includes a plurality of(for example, three colors of red, green, and blue) colored layers 42.Particles (for example, pigments) which may be ionized and may dissolvein the liquid crystal 20 are dispersed in the colored layers 42.

The color filter layer 40 includes a first region 44 formed of onecolored layer 42. In the color filter layer 40, the colored layers 42having different colors are arranged adjacent to one another. In thefirst region 44, the color filter layer 40 executes an original functionof the color filter (function of transmitting light merely of particularcolor).

The color filter layer 40 also includes a second region 46 formed oflaminated colored layers 42 including two or more layers (three layersin FIG. 4) having different colors. In the second region 46, two coloredlayers 42 having different colors are arranged adjacent to each otherand end portions thereof are formed so as to overlap with each other. Inaddition, in the example illustrated in FIG. 4, the colored layer 42 ofanother color is further overlapped thereon.

In the second region 46, a convex portion 48 (portion higher thanportion where one colored layer 42 is provided) is formed of thelaminated plurality of colored layers 42 having different colors. By theconvex portion 48, a gap between the first substrate 16 and the secondsubstrate 18 may be retained.

An electrode structure layer 50 is formed between the liquid crystal 20and the color filter layer 40. The electrode structure layer 50generates an electric field which is parallel to the surface of thefirst substrate 16 by an applied voltage, so as to drive the liquidcrystal 20. That is, an in-plane switching (IPS) type liquid crystaldisplay device is employed in this embodiment.

The electrode structure layer 50 includes a transparent insulating film52 formed of a semiconductor oxide (for example, SiO₂) or asemiconductor nitride (for example, SiN) by, for example, plasma CVD, soas to separate the surfaces of the liquid crystal 20 and the colorfilter layer 40 facing each other. The transparent insulating film 52serves as a barrier layer, which prevents the particles (for example,pigments) dispersed in the colored layers 42 or the black matrix 38 frombeing dissolved in the liquid crystal 20.

The electrode structure layer 50 further includes a first transparentconductive film 54 and a second transparent conductive film 56 which areboth formed of an oxide semiconductor and formed on both surfaces of thetransparent insulating film 52, respectively. The first transparentconductive film 54 and the second transparent conductive film 56 may beformed of indium tin oxide (ITO) or indium zinc oxide by, for example,sputtering. Further, the first transparent conductive film 54 and thesecond transparent conductive film 56 may be formed of a plurality oflayers.

A lateral electric field is generated by the voltage applied between thefirst transparent conductive film 54 and the second transparentconductive film 56. For example, the first transparent conductive film54 constitutes a common electrode and the second transparent conductivefilm 56 constitutes a pixel electrode. Further, the first transparentconductive film 54 and the second transparent conductive film 56 serveas a barrier layer together with the transparent insulating film 52 andprevent the particles (for example, pigments) dispersed in the coloredlayers 42 or the black matrix 38 from being dissolved in the liquidcrystal 20.

Note that, on the surface of the second substrate 18 facing the liquidcrystal 20, an overcoat film 58 is formed, which is formed of an organicmaterial and covers flaws generated on the surface of the secondsubstrate 18. The overcoat film 58 does not include a contaminationsource which may be ionized and may dissolve in the liquid crystal 20such as a pigment, and is formed of a transparent material.

According to this embodiment, the transparent insulating film 52, thefirst transparent conductive film 54, and the second transparentconductive film 56 of the electrode structure layer 50 may prevent thematerials dispersed in the colored layers 42 from being dissolved in theliquid crystal 20. Therefore, changes in conductivity and dielectricconstant due to contaminated liquid crystal 20 do not occur. Further,the transparent insulating film 52, the first transparent conductivefilm 54, and the second transparent conductive film 56 are membersoriginally necessary for driving the liquid crystal 20, and hence it isunnecessary to add another member.

The electrode structure layer 50 covers the entire color filter layer40. In a portion where the electrode structure layer 50 covers thesecond region 46 (laminated colored layers 42 having different colors)of the color filter layer 40, the transparent insulating film 52, thefirst transparent conductive film 54, and the second transparentconductive film 56 are formed continuously.

In a portion where the electrode structure layer 50 covers the firstregion 44 of the color filter layer 40, a first through hole 60 isformed in communication with the first transparent conductive film 54and the transparent insulating film 52. Further, a second through hole62 is formed in communication with the colored layer 42 formed of onelayer and the insulating layer 36. The first through hole 60 and thesecond through hole 62 are in communication with each other. A part ofthe second transparent conductive film 56 enters the first through hole60 and the second through hole 62, to thereby be electrically connectedto the source electrode 32. Further, as illustrated in FIG. 4, a notch,a slit, or a hole may be formed also in the second transparentconductive film 56 if needed. Above the color filter layer 40 in thefirst region 44, the transparent insulating film 52 is always present.However, the electrode structure layer 50 has a portion without at leastone of the first transparent conductive film 54 and the transparentinsulating film 52.

This embodiment further includes well-known structures of the liquidcrystal display device (for example, alignment film), but a detaileddescription thereof is omitted herein.

Second Embodiment

FIG. 5 is a plan view illustrating a part of a liquid crystal displaypanel of a liquid crystal display device according to a secondembodiment of the present invention. FIG. 6 is a cross-sectional view ofthe liquid crystal display panel taken along the line VI-VI of FIG. 5.

This embodiment differs from the first embodiment in that a black matrix138 is formed between the liquid crystal 20 and the second substrate 18(specifically, between liquid crystal 20 and overcoat film 158). Theblack matrix 138 also contains a pigment (for example, carbon), and theovercoat film 158 prevents the pigment from being dissolved in theliquid crystal 20. Other details of this embodiment correspond to thecontents described in the first embodiment.

The present invention is not limited to the embodiments described above,and various modifications may be made thereto. For example, thestructures described in the embodiments may be replaced by substantiallythe same structure, a structure having the same action and effect, and astructure which may achieve the same object.

What is claimed is:
 1. A liquid crystal display device, comprising: afirst substrate; a second substrate; a liquid crystal provided betweenthe first substrate and the second substrate; a thin film transistorformed on a surface of the first substrate facing the liquid crystal; acolor filter layer formed between the liquid crystal and the thin filmtransistor; and an electrode structure layer formed between the liquidcrystal and the color filter layer; wherein the electrode structurelayer includes: a transparent insulating film being formed so as toseparate a surface of the liquid crystal and a surface of the colorfilter layer facing each other; and a first transparent conductive filmand a second transparent conductive film arranged with respect to thetransparent insulating film so that the first and second transparentconductive films are formed on opposite sides of the transparentinsulating film, respectively; wherein the color filter layer includes:a first region formed of one colored layer of a plurality of differentcolored layers; and a second region formed of at least two laminateddifferent colored layers of the plurality of different colored layers,the second region having a convex portion formed therein, and the convexportion retaining a gap formed between the first substrate and thesecond substrate; wherein the arrangement of the first transparentconductive film, the transparent insulating film and the secondtransparent conductive film is disposed between the liquid crystal andan upper surface of the color filter layer in the vertical direction;and wherein the first transparent conductive film covers the uppersurface of the color filter layer in both of the first region and thesecond region.
 2. The liquid crystal display device according to claim1, further comprising a black matrix formed between the color filterlayer and the thin film transistor.
 3. The liquid crystal display deviceaccording to claim 1, further comprising a black matrix formed betweenthe liquid crystal and the second substrate.